Wednesday, May 8, 2013

How Does Overcharging Damage Batteries?

Overcharging a battery occurs when the total capacity drained has been replaced by recharging, but the battery remains on charge. Overcharging creates excessive heat which can cause the battery plates within the cells to buckle and shed their active material. A battery will react to the overcharge by producing an excessive amount of hydrogen and oxygen. These gases are the result of the breakdown of the water molecules within the electrolyte. The water that has been displaced by overcharging can be replaced in a wet (non-sealed) battery, but, in maintenance-free sealed lead batteries, NiCad, NiMH permanent capacity loss will result. A good charger has built in circuitry that senses the battery state and converts to a lower trickle charge so as not to over heat the battery. Excessive discharging can also damage a battery. The amount of discharge a battery can have without damage depends upon the chemistry of the battery. In general, a lead acid battery can not tolerate as deep a discharge as a NiCad battery or NiMH battery. Sealed lead acid batteries function best if they are discharged to only about 85% of nominal voltage (10.2V on 12V battery). NiCad & NiMH are good for two way radios because they can be deeply discharged and recharged.